A major emphasis of this project is the determination of the amino acid sequence of pregnant mare serum gonadotropin. The sequence of the alpha subunit is complete and comparisons with other species are possible. The beta subunit has approximately 20% of the residues yet to place. Using acylation, and/or selective reactivity of various functional groups of the isolated subunits of ovine lutropin, studies are continuing for evaluating the essential nature of specific groups in the molecule, both with respect to subunit recombination or receptor site binding. Using radioligand assays and in vitro steroidogenesis assays, the foregoing approaches are being used to evaluate the molecular parameters for lutropin and follitropin activity as correlated for amino acid sequence and functional group sensitivities.